1. Field of Invention
The present invention relates to novel photosensitive compounds and novel photosensitive compositions based thereon as well as to novel photographic processes employing these compositions and more specifically to high-resolution photographic reproduction processes not requiring wet development.
2. Discussion of the Prior Art
Photographic reproduction processes using silver halide emulsions are well known and widely used for such purposes as reproduction of documents, e.g. microfilms. However, in addition to requiring a wet chemical development process, i.e. liquid developing solutions, silver halide emulsion type photographic processes have the additional disadvantage of graininess in the developed print and therefore are subject to only a limited resolution power.
Electrophotographic processes are also disadvantageous since they only have a low sensitivity, introduce graininess in the developed image, and require for development, addition of toner materials in the form of powders or liquid.
Thermographic reproduction processes are also well known in the prior art but are subject to even lower sensitivities than electrophotographic processes. And, although the emulsions typically used in thermographic reproduction are not grain emulsions, the use of infrared exposure during the reproduction process results in heat diffusion and deterioration of the resolution power of the emulsion. Moreover, thermographic processes have the additional drawback of not being able to reproduce all colors.
Diazo-type printing processes have been used for many years and have been used in several forms, most notable of which are the negative diazo-type processes and the positive diazo-type processes. Exemplary of the former process is the image-wise exposure of a diazo film layer containing a light-sensitive diazonium compound and a mercurous salt. This process results in grainless silver images of high resolving power and requires physical development in which exposure requires only a far smaller quantity of light energy than several other diazo-type processes. The negative type processes have not, however, become commercially successful.
The positive diazo type processes have become increasingly popular due to their high contrast and the short and simple after treatments required to obtain direct positive copies which are particularly adaptable for such uses as the reproduction of line originals such as tracings and in preparation of maps and similar sketches. Typical of the positive diazo-type processes are the two component or "dry" treatments in which a suitable substrate is coated with a light-sensitive diazonium compound and a coupler compound, usually in the presence of a stabilizing acid to prevent premature coupling; after exposure to light through a transparency or the original work, development takes place by contact with an alkaline material, generally anhydrous ammonia. In the semi-dry process, the substrate only contains the photosensitive diazonium compound; after image-wise exposure to light, the substrate is developed by contact with an alkaline developing solution which contains the coupler compound. The third most widely used positive diazo-type process is the heat developable process in which the diazonium compound and the coupler compound are again combined on the substrate in an acid medium containing a base releasing agent which, after the substrate is image-wide exposed to a light source, a heat treatment is administered which results in the production of an alkaline environment which allows the coupler compound and diazonium compound to react and form the dye image.
Each of the different positive processes, however, have been subject to various drawbacks. For example, the dry processes are subject to the problem that with most diazonium compounds and couplers, the waterfastness of the prints obtained is unsatisfactory for many purposes because of the problems in storage of the finished product and the inability to wash the finished product. Moreover, in the production of red or reddish brown prints, the most typically used couplers, amides of 3,5-dihydroxy benzoic acid of the thiazole or selenazole derivatives of these amides only exhibit slight water solubility and makes the use of these compounds difficult. Also, the emulsions used in the heat developable processes remain stable for only relatively short periods.
Some of the foregoing drawbacks have been eliminated in a dry, heat development process using heat sensitive compositions formed with a base of known spiropyrans (as disclosed for example, in J. H. Day, Chem. Rev., 63, 65 (1963) which will decompose upon the application of heat into merocyanines (e.g. merocyanine of 6'chloro-8'-methoxy-benzoindolino pyrylospirane) and phenols which will, when in the molten or dissolved state, react with each other to produce a colored complex. However, because photographic processes based on these spiropyrans require a local heating of the heat-sensitive composition in order to obtain a colored image or line, their use is very complex. In practice, their use is limited to the field of graphic recordings, for example, in recording apparatus using a hot stylus or the like as a means of local heating.